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[PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature

Kai Huang posted 8 patches 1 year, 3 months ago
There is a newer version of this series
[PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature
Posted by Kai Huang 1 year, 3 months ago 
Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
RBP is used as frame pointer in the x86_64 calling convention, and
clobbering RBP could result in bad things like being unable to unwind
the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
gap.

A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
metadata field via bit 18.

Don't initialize the TDX module if this feature is not supported [1].

Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]
Signed-off-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
---

v2 -> v3:
 - check_module_compatibility() -> check_features().
 - Improve error message.

 https://lore.kernel.org/kvm/cover.1721186590.git.kai.huang@intel.com/T/#md9e2eeef927838cbf20d7b361cdbea518b8aec50

---
 arch/x86/virt/vmx/tdx/tdx.c | 17 +++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx.h |  3 +++
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index fa335ab1ae92..032a53ddf5bc 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -454,6 +454,18 @@ static int get_tdx_sys_info(struct tdx_sys_info *sysinfo)
 	return get_tdx_sys_info_tdmr(&sysinfo->tdmr);
 }
 
+static int check_features(struct tdx_sys_info *sysinfo)
+{
+	u64 tdx_features0 = sysinfo->features.tdx_features0;
+
+	if (!(tdx_features0 & TDX_FEATURES0_NO_RBP_MOD)) {
+		pr_err("frame pointer (RBP) clobber bug present, upgrade TDX module\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 /* Calculate the actual TDMR size */
 static int tdmr_size_single(u16 max_reserved_per_tdmr)
 {
@@ -1235,6 +1247,11 @@ static int init_tdx_module(void)
 
 	print_basic_sys_info(&sysinfo);
 
+	/* Check whether the kernel can support this module */
+	ret = check_features(&sysinfo);
+	if (ret)
+		return ret;
+
 	/*
 	 * To keep things simple, assume that all TDX-protected memory
 	 * will come from the page allocator.  Make sure all pages in the
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index e7bed9e717c7..831361e6d0fb 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -154,6 +154,9 @@ struct tdx_sys_info_features {
 	u64 tdx_features0;
 };
 
+/* Architectural bit definitions of TDX_FEATURES0 metadata field */
+#define TDX_FEATURES0_NO_RBP_MOD	_BITULL(18)
+
 /* Class "TDX Module Version" */
 struct tdx_sys_info_version {
 	u16 major;
-- 
2.46.0
Re: [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature
Posted by Dan Williams 1 year, 3 months ago 
How about:

    Subject: x86/virt/tdx: Require the module to assert it has the NO_RBP_MOD mitigation

...to avoid the double negative.

Kai Huang wrote:
> Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
> RBP is used as frame pointer in the x86_64 calling convention, and
> clobbering RBP could result in bad things like being unable to unwind
> the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
> gap.
> 
> A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
> not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
> metadata field via bit 18.
> 
> Don't initialize the TDX module if this feature is not supported [1].
> 
> Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]

Trim this to the direct message-id format, but otherwise:

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Re: [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature
Posted by Huang, Kai 1 year, 3 months ago 
On Fri, 2024-09-06 at 16:36 -0700, Dan Williams wrote:
> How about:
> 
>     Subject: x86/virt/tdx: Require the module to assert it has the NO_RBP_MOD mitigation
> 
> ...to avoid the double negative.

Will do.  Thanks.

> 
> Kai Huang wrote:
> > Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
> > RBP is used as frame pointer in the x86_64 calling convention, and
> > clobbering RBP could result in bad things like being unable to unwind
> > the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
> > gap.
> > 
> > A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
> > not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
> > metadata field via bit 18.
> > 
> > Don't initialize the TDX module if this feature is not supported [1].
> > 
> > Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]
> 
> Trim this to the direct message-id format, but otherwise:

Will do.  If I got it right, the link with message-id should be:

https://lore.kernel.org/all/fc0e8ab7-86d4-4428-be31-82e1ece6dd21@intel.com/

> 
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>

Thanks.
Re: [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature
Posted by Adrian Hunter 1 year, 3 months ago 
On 27/08/24 10:14, Kai Huang wrote:
> Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
> RBP is used as frame pointer in the x86_64 calling convention, and
> clobbering RBP could result in bad things like being unable to unwind
> the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
> gap.
> 
> A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
> not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
> metadata field via bit 18.
> 
> Don't initialize the TDX module if this feature is not supported [1].
> 
> Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
> 
> v2 -> v3:
>  - check_module_compatibility() -> check_features().
>  - Improve error message.
> 
>  https://lore.kernel.org/kvm/cover.1721186590.git.kai.huang@intel.com/T/#md9e2eeef927838cbf20d7b361cdbea518b8aec50
> 
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 17 +++++++++++++++++
>  arch/x86/virt/vmx/tdx/tdx.h |  3 +++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index fa335ab1ae92..032a53ddf5bc 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -454,6 +454,18 @@ static int get_tdx_sys_info(struct tdx_sys_info *sysinfo)
>  	return get_tdx_sys_info_tdmr(&sysinfo->tdmr);
>  }
>  
> +static int check_features(struct tdx_sys_info *sysinfo)
> +{
> +	u64 tdx_features0 = sysinfo->features.tdx_features0;
> +
> +	if (!(tdx_features0 & TDX_FEATURES0_NO_RBP_MOD)) {
> +		pr_err("frame pointer (RBP) clobber bug present, upgrade TDX module\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  /* Calculate the actual TDMR size */
>  static int tdmr_size_single(u16 max_reserved_per_tdmr)
>  {
> @@ -1235,6 +1247,11 @@ static int init_tdx_module(void)
>  
>  	print_basic_sys_info(&sysinfo);
>  
> +	/* Check whether the kernel can support this module */
> +	ret = check_features(&sysinfo);
> +	if (ret)
> +		return ret;
> +
>  	/*
>  	 * To keep things simple, assume that all TDX-protected memory
>  	 * will come from the page allocator.  Make sure all pages in the
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index e7bed9e717c7..831361e6d0fb 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -154,6 +154,9 @@ struct tdx_sys_info_features {
>  	u64 tdx_features0;
>  };
>  
> +/* Architectural bit definitions of TDX_FEATURES0 metadata field */
> +#define TDX_FEATURES0_NO_RBP_MOD	_BITULL(18)
> +
>  /* Class "TDX Module Version" */
>  struct tdx_sys_info_version {
>  	u16 major;

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